1. Field of the Invention
This invention generally relates to an electric discharge device and a method of using the electric discharge device. More specifically, the present invention relates to an apparatus and method of performing a hole forming process on a workpiece by utilizing an electric discharge device.
2. Background Information
An electric arc discharge process is often used to cut or form holes in a metal workpiece. Specifically, an arc voltage charging device is connected between an electrode and a workpiece. Current flows from the arc voltage charging device to the electrode. When the electrode is located adjacent the workpiece, an arc is formed between the electrode and the workpiece such that current passes from the electrode through the workpiece and back to the arc voltage charging device. The arc from the electrode then causes material of the workpiece to be eroded away. The workpiece is often processed under an insulating liquid, with intermittent electric arcs occurring between the electrode and the workpiece under the insulating liquid. The conventional electric discharge methods used to form a hole in a workpiece have many advantages over conventional mechanical methods of forming a hole. For example, prior art electric discharge processes typically do not create burrs during the formation of holes. Moreover, these prior art electric discharge processes can typically form diagonal holes without any difficulty. These prior art electric discharge processes can also be used to process workpieces made of very hard rigid material.
An example of a conventional electric arc discharge process is diagrammatically illustrated in FIGS. 1 and 2. As seen in FIG. 2, a hole is formed in a workpiece 1 using a long cylindrical discharging electrode 2. The diameter of the electrode 2 is sized to correspond to the diameter of the hole to be formed. This discharging electrode 2 is cylindrical and has an internal pathway 2a through which processing liquid flows. The hole is formed in the workpiece as the discharging electrode 2 is moved downwardly towards the workpiece with the processing liquid being supplied through the pathway 2a.
When a hole forming process is performed with a processing liquid being supplied to the above-described discharging electrode 2, a sludge or process powder is formed. The sludge or process powder from the workpiece is disposed of by the processing liquid, which flows upwardly around the discharging electrode 2. This disposal of the sludge or process powder occurs until the hole formed in the workpiece 1 by the discharging electrode 2 passes through the workpiece 1.
However, as shown in FIG. 2, when the discharging electrode 2 passes through the workpiece 1, the processing liquid starts to flow out of the hole, which decreases the pressure of the processing liquid. Also, the sludge or process powder builds up around the electrode since it is no longer being properly disposed of by the processing liquid. Furthermore, the electric discharge between the electrode 2 and the workpiece 1 becomes unstable because the arc or electric discharge is occurring in the air instead of under the processing liquid. The discharging electrode 2 is moved downward by a servo-actuated control. When electric discharge or arcs becomes unstable, the discharging electrode 2 goes down less smoothly. As a result, just prior to completion of the hole forming process, the discharging electrode 2 keeps moving up and down, which lengthens the time to complete the hole forming process.
To solve such problems, prior art electric arc discharging devices blow compressed air from beneath the processing hole to keep the processing liquid from escaping out of the bottom of the processing hole. Although this method prevents arcs or electric discharges from occurring in the absence of the processing liquid, it still does not stabilize the pressure of the processing liquid. Therefore it is difficult for electric discharges or arcs to take place under the most desirable conditions.
In view of the above, there exists a need for electric discharge device which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.